First, I appreciated the thoughtful responses I received to my previous post. To those of you who referred me to the avweb and other articles, thank you. I read them, and was just about convinced, until I went back and looked at a Continental bulletin, Sid 97-2, dated 2-17-97. Let me quote:
"The highest combustion temperatures occur near the ideal fuel/air ratio of about one pound of fuel for 15 pounds of air. Combustion temperatures drop on both the lean side and rich side of this point. However,on the lean side of peak the reduction in power with leaning is rapid and lean misfire occurs on many engines about 100 degrees lean of peak. On the rich side power is very stable with changes in fuel flow. This characteristic allows the engine to obtain rated power with rich mixtures where the combustion temperatures are substantially reduced. This additional fuel at takeoff is required to maintain control of cylinder structure and oil cooling.
In cruise, operating rich reduces combustion temperatures and should be used to control engine temperatures. For maximum range, operation on the lean side of peak or at peak is permitted at low cruise power on some engine models. For normal operation, it is good practice that mixtures be controlled so that the hot cylinder is 50 to 100 degrees rich of peak at cruise settings . . . "
So, here I sit, absent engine monitor and confused as ever. Who’s a poor middle-aged midwesterner to believe, mechanics, the articles, or the technical bulletin of the engine manufacturer.
Which opinion do you find most reliable, and how are those of you with IO-360s currently operating them?
The “rich or lean of peak” debate is really academic in the absence of adequate engine monitoring instrumentation. When you attempt to lean using a single probe EGT you really don’t know when the leanest cylinder reaches peak. Assume that the single probe EGT is connected to the cylinder that USUALLY is the leanest (i.e. reaches peak first) in that engine/airframe installation). Now assume that there is some debris in a fuel injector to a different cylinder. As you lean, the cylinder with the restricted fuel flow will peak first. Unfortunately you won’t know it. If you continue to lean by the EGT you will make the REAL leanest cylinder progressively more lean of peak. If you believe in operation 50 lean of peak, by the time you reach it using the single probe EGT you may have one or more of your cylinders way leaner than that. That’s a setup for rough operation and preignition. Therefore, with a single probe EGT the CONSERVATIVE way to lean is to find peak and enrich at least 50 or 75 to the rich side of peak. That was if there are any cylinders that are leaner than you thought they will be brought back into a safe operating range. I think that’s why so many mechanics and the engine people tell you to do that. It really is the most conservative method. While it may result in some increased plug fouling and higher CHTs that may eat away at your TBO it is less likely to result in the sort of damage that can ruin an engine in a few minutes.
On the other hand if you have a multiprobe EGT/CHT (and we really need this on the ARNAV or a stand alone GEM or JPI system)- then you can find the leanedt cylinder with absolute accuracy (it’s the one that reaches peak first when you lean). Then it’s probably OK to run it a little lean of peak. But you then know that none of your cylinders are leaner than 50 lean of peak and you can also monitor all the CHTs as well. I really think that a multiprobe engine monitoring system should be mandatory on all piston aircraft with higher compression, fuel injected engines.
By the way, has anybody heard about the engine monitoring installation that was supposed to be done last weekend by ARNAV?
Jerrold Seckler SR22 #69
First, I appreciated the thoughtful responses I received to my previous post. To those of you who referred me to the avweb and other articles, thank you. I read them, and was just about convinced, until I went back and looked at a Continental bulletin, Sid 97-2, dated 2-17-97. Let me quote:
"The highest combustion temperatures occur near the ideal fuel/air ratio of about one pound of fuel for 15 pounds of air. Combustion temperatures drop on both the lean side and rich side of this point. However,on the lean side of peak the reduction in power with leaning is rapid and lean misfire occurs on many engines about 100 degrees lean of peak. On the rich side power is very stable with changes in fuel flow. This characteristic allows the engine to obtain rated power with rich mixtures where the combustion temperatures are substantially reduced. This additional fuel at takeoff is required to maintain control of cylinder structure and oil cooling.
In cruise, operating rich reduces combustion temperatures and should be used to control engine temperatures. For maximum range, operation on the lean side of peak or at peak is permitted at low cruise power on some engine models. For normal operation, it is good practice that mixtures be controlled so that the hot cylinder is 50 to 100 degrees rich of peak at cruise settings . . . "
So, here I sit, absent engine monitor and confused as ever. Who’s a poor middle-aged midwesterner to believe, mechanics, the articles, or the technical bulletin of the engine manufacturer.
Which opinion do you find most reliable, and how are those of you with IO-360s currently operating them?
Dave - Jerrold is right on target. I have installed a 6 probe GEM monitor with a separate display. The display head is located right next to the flap switch so that it is easy to see when leaning. Now that I’ve had it for a little while I still like the location.
More to the point, however, is the differences in EGT temps amoung the various cyclinders can be stark! I consistently have the number #3 cyclinder indicate a higher EGT temp than the others … by about 25 to 50 degrees. That is enough of a difference to make me nervous about leaning lean of peak (LOP). However, when I lean to LOP, I continue to lean until the last cyclinder is 50 degrees LOP.
Having said all that, I rarely use LOP leaning because of the loss of power and SPEED! I hate to go slow so I almost always go ROP! I don’t know about you, but I bought this plane to go fast on a budget! LOP is a money saver with less fuel burn, but my budget is not that tight … I may have to reasses after checking the stock market values at month end 
The point is that I suspect most of us will want whatever we can get in terms of speed regardless of fuel burn.
Some have asked about performance numbers. My trusty and OLD 1999 SR20 gets consistently about 158 TAS at about 11 GPH while “spinning” about 2500 RPM. Generally, I see 153-156 TAS ranges at 7000 to 8000 MSL with fuel flow about 10 to 11 GPH. If I use LOP at those altitudes, I see speeds of about 145-148 TAS with fuel flows of about 8.5 to 9.5 GPH. The local FBO, Del Monte, is annoyed with me that I don’t burn more fuel. 
Lycoming even goes so far in one of its online technical bulletins (carbureted engine 0-360) to say that you are almost better off not even using the EGT since, like you say, it only measures one cylinder. Perhaps, the wrong one. If you lean to a little roughness, they say, then you know that the leanest cylinder is starting to misfire. Then, enrichen slightly to smoothness. Isn’t this what your instructor always said? Perhaps, Continentals are different, especially with fuel injection. Anyway, a single probe EGT seems to be almost useless, although better with metered fuel injection to each cylinder than my Lycoming O-360.